With reference to FIG. 1, a typical turbocharger 101 has a turbine that includes a turbocharger housing and a rotor configured to rotate within the turbocharger housing around an axis of rotor rotation 103 on oil-lubricated thrust bearings and two sets of oil-lubricated journal bearings (one for each respective rotor wheel), or alternatively, other similarly supportive bearings. The turbocharger housing includes a turbine housing 105, a compressor housing 107, and a center housing 109 (i.e., a bearing housing that contains the bearings) that connects the turbine housing to the compressor housing. The rotor includes a turbine wheel 111 located substantially within the turbine housing, a compressor wheel 113 located substantially within the compressor housing, and a shaft 115 extending along the axis of rotor rotation, through the center housing, to connect the turbine wheel to the compressor wheel.
The turbine housing 105 and turbine wheel 111 form a turbine configured to circumferentially receive a high-pressure and high-temperature exhaust gas stream 121 from an engine, e.g., from an exhaust manifold 123 of an internal combustion engine 125. The turbine wheel (and thus the rotor) is driven in rotation around the axis of rotor rotation 103 by the high-pressure and high-temperature exhaust gas stream, which becomes a lower-pressure and lower-temperature exhaust gas stream 127 and is axially released into an exhaust system (not shown).
The compressor housing 107 and compressor wheel 113 form a compressor stage. The compressor wheel, being driven in rotation by the exhaust-gas driven turbine wheel 111, is configured to compress axially received input air (e.g., ambient air 131, or already-pressurized air from a previous-stage in a multi-stage compressor) into a pressurized air stream 133 that is ejected circumferentially from the compressor. Due to the compression process, the pressurized air stream is characterized by an increased temperature over that of the input air.
Optionally, the pressurized air stream may be channeled through a convectively cooled charge air cooler 135 configured to dissipate heat from the pressurized air stream, increasing its density. The resulting cooled and pressurized output air stream 137 is channeled into an intake manifold 139 on the internal combustion engine, or alternatively, into a subsequent-stage, in-series compressor. The operation of the system is controlled by an ECU 151 (engine control unit) that connects to the remainder of the system via communication connections 153.
It is desirable to limit axial loads on the rotor to minimize the size and cost of the axial bearings, while maximizing their reliability. One way to do this is to use two-sided wheels. Other means are also known to those of skill in the art.
For turbines, one cause of axial loads is the leaking of radially (and circumferentially) supplied high-pressure exhaust gas from the inducer of the turbine around to a back-disk area of a turbine wheel. This leaked high-pressure exhaust gas behind the turbine wheel can place axial loads on the wheel that far exceed the axial forces of the exhaust gas that passes through an exducer of the radial turbine.
Accordingly, there has existed a need for a turbocharger turbine minimizing high and low pressure flow in back-disk regions behind radial turbines and radial compressors. Preferred embodiments of the present invention satisfy these and other needs, and provide further related advantages.